(i) Field of the Invention
This invention relates to emulsifying compositions and more particularly, to emulsifying compositions of the type which comprises alkyl or alkenyl glyceryl ether phosphates or salts thereof and which exhibits reduced irritativeness against living body and particularly skin and has the excellent emulsification stabilizing ability.
(ii) Description of the Prior Art
In general, compounds used as an emulsifier for emulsifying composition can broadly be classified into two categories including a hydrophilic emulsifier group which shows high solubility in water or has high HLB values and an oleophilic emulsifier group which shows high solubility in oil or has small HLB values. The hydrophilic emulsifier group has been utilized for stabilizing chiefly oil-in-water type (O/W type) emulsions while the oleophilic emulsifier group utilized for stabilizing water-in-oil type (W/O type) emulsions. In this connection, however, oils greatly differ in property depending on the type of oil and thus an HLB value required for the emulsification depends on the type of an oil to be emulsified. Accordingly, it is general that hydrophilic emulsifiers and oleophilic emulsifiers are hardly employed singly, but both the emulsifiers are mixed to properly adjust the HLB value for emulsification. This is true especially when oils to be emulsified are in mixed form.
Conventionally employed hydrophilic emulsifiers are, for example, anionic surface active agents such as alkali metal salts of fatty acids, alkylsulfates and the like, ethylene oxide-added nonionic active agents such as polyoxyethylene alkyl ethers, polyoxyethylene-fatty acid esters, polyoxyethylene sorbitan-fatty acid esters and the like. On the other hand, oleophilic emulsifiers are, for example, nonionic surface active agents such as sorbitan-fatty acid esters, glycerine-fatty acid esters and the like.
Emulsifier compositions which are obtained by mixing hydrophilic emulsifiers, which are combinations of fatty acid-triethanolamine salts and ethylene oxide-added nonionic surface active agents with oleophilic emulsifiers such as glycerine-fatty acid esters to have various levels of HLB values are very stable in emulsification stability, so that they have widely utilized in the field of cosmetics such as creams.
However, it is suggested that ethylene oxide addition-type nonionic surface active agents contain formalin, dioxane and the like as impurities and these impurities have the allergic action on living body. In addition, it is known that anionic surface active agents generally produce high skin irritation and are thus not favored as an emulsifier. Accordingly, it is the common practice to use as the anionic surface active agent alkali metal salts of fatty acids which produce relatively low skin irritation, with the attendant disadvantage that the resulting emulsion becomes alkaline in nature.
On the other hand, it is known that there are present in the living body a group of compounds called phospholipids which possess surface active properties and that they play a very important role as the main components of membranes of the living body. Typical examples of the phospholipid include glycerophospholipids such as phosphatidyl choline (lecithin), phosphatidyl ethanolamine (cephalin), phosphatidyl serine and the like. These phospholipids are components in vivo and are surface active materials which are highly safe for use on the living body. For instance, lecithin has been industrially utilized as an emulsifier. However, these are of natural origin and have various impurities and suffer deterioration in quality inherent of natural materials with the passage of time. Furthermore, the structure such as that of a fatty acid composition cannot be arbitrarily changed, so that its HLB value cannot also be changed freely with unsatifactory emulsifying activity. Thus, they are not satisfactory for use as an emulsifier and have limitations in application.